Method for forming double density wordline

ABSTRACT

A method for forming a double density wordline. A semiconductor substrate having a poly layer, a first insulating layer, a first dummy poly layer, and a second insulating layer is provided. The second insulating layer and the first dummy poly layer separated by an opening are a first wordline mask and a second wordline mask respectively. A spacer is formed on a sidewall of the opening, and the opening is filled with a second dummy poly layer. The spacer, the second insulating layer, and the exposed first insulating layer are removed to form a third wordline mask, the third wordline is composed of the second dummy poly layer and the unexposed first insulating layer. The poly layer is etched to form a first wordline, a second wordline, and a third wordline using the first wordline mask, the second wordline mask, and the third wordline mask as etching masks.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to an EEPROM process, and more particularlyto a method to increase wordline density by reducing wordline widths ofand space therebetween.

[0003] 2. Description of the Related Art

[0004] Digital information is stored in a memory cell wherein the memorycell acts as a single digital bit. Hence, a plurality of digital bits isstored in a plurality of memory cells. The memory cells are arranged bearray, and each memory cell is set at predetermined address by columnand row. The memory cells in the same column or row are strung togetherwith the same conducting wire which is called a wordline.

[0005]FIGS. 1a to 1 b are cross-sections of the conventional method forforming wordlines of an EEPROM.

[0006] In FIG. 1a, a semiconductor substrate 101 is provided, and aplurality of memory cells and other elements can be formed thereon. Apoly layer 102, a WSi layer 103, a patterned photoresist layer 104 withan opening 105 are sequentially formed in the semiconductor substrate101. The width of the opening 105 is 0.18 μm, and a portion of thesurface of the WSi layer 103 is exposed by the opening 105.

[0007] In FIG. 1b, the WSi layer 103 and the poly layer 102 areanisotropically etched using the patterned photoresist layer 104 as anetching mask until the semiconductor substrate 101 is exposed to form anopening 106. After the photoresist layer 104 is removed, wordlines 107 aand 107 b are formed and separated by the opening 106. The widths of thewordlines 107 a and 107 b are both 0.14 μm. The size of the opening 106matches the size of the opening 105 of the patterned photoresist layer104.

[0008] Due to the restrictions of the characteristics of the lightsource and the photoresist layer, an insufficiently thick photoresistlayer with cannot effectively isolate the etching source. Conversely,when an excessively thick photoresist layer is used, the size of thecontact window is difficult to control. Possible collapse of thephotoresist layer should also be prevented.

SUMMARY OF THE INVENTION

[0009] The present invention provides a method for forming a wordline ofan EEPROM by an additional wordline mask to reduce wordline widths andthe space therebetween.

[0010] Accordingly, the present invention provides a method for forminga double density wordline. A semiconductor substrate is provided. A polylayer, a first insulating layer, a first sacrificial layer, a secondinsulating layer, and a photoresist layer with a wordline pattern aresequentially formed thereon, and a portion of the second insulatinglayer is exposed by the wordline pattern. The insulating layer and thefirst sacrificial layer are sequentially etched using the photoresistlayer as an etching mask until the first insulating layer is exposed toform a first word line mask, a second wordline mask, and an openingtherebetween. The photoresist layer is removed. A spacer is formed on asidewall of the opening. The opening is filled with a second sacrificiallayer. The spacer, the second insulating layer, and the first insulatinglayer under the spacer to form a third wordline mask composed of thesecond sacrificial layer and the first insulating layer thereunder. Thepoly layer is etched using the first wordline mask, the second wordlinemask, and the third wordline mask as etching masks to form a firstwordline, a second wordline, and a third wordline.

[0011] Accordingly, the present invention also provides a method forforming a double density wordline. A semiconductor substrate with a polylayer, a silicide layer, an oxide layer, a first dummy poly layer, and afirst nitride layer is provided. A patterned photoresist layer with afirst opening is formed on the first nitride layer, and a portion of thefirst nitride layer is exposed by the first opening. The first nitrideand the first dummy poly layer are sequentially etched until the oxidelayer is exposed to form a first wordline mask, a second wordline mask,and a second opening therebetween. The patterned photoresist layer isremoved. A second nitride layer is conformably formed to cover the firstwordline mask, the second wordline mask, and the second opening. Thesecond nitride layer is anisotropically etched to form a spacer on asidewall of the second opening. A second dummy poly layer is formedcover the first wordline mask, the second wordline mask, and the secondopening, and the second opening is filled with the second dummy polylayer. The second dummy poly layer is etched to a level below thespacer. After the spacer, the first nitride layer, and the exposed oxidelayer are removed, a third wordline mask is composed of the second dummypoly layer and the oxide layer thereunder. The silicide layer and thepoly layer are sequentially etched using the first wordline mask, thesecond wordline mask, and the third wordline mask as etching masks toform a first wordline, a second wordline, and a third wordline.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a better understanding of the present invention, reference ismade to a detailed description to be read in conjunction with theaccompanying drawings, in which:

[0013]FIGS. 1a to 1 b are cross-sections of the conventional method forforming wordlines of an EEPROM;

[0014]FIGS. 2a to 2 h are cross-sections of the method for forming thedouble density wordline of an EEPROM of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015]FIGS. 2a to 2 h are cross-sections of the method for formingdouble density wordline of an EEPROM of the present invention.

[0016] In FIG. 2a, a semiconductor substrate 201 is provided, aplurality of memory cells and other elements can be formed thereon.

[0017] A poly layer 202, a metal layer 203, an insulating layer 204, afirst dummy poly layer 205 acting as a sacrificial layer, a insulatinglayer 206, and a patterned photoresist layer 207 with an opening 208 aresequentially formed on the semiconductor substrate 201, and a portion ofthe insulating layer 206 is exposed by the opening 208. The thickness ofthe poly layer 202 is about 1150 to 1250 Å. The metal layer 203 can be asilicide layer, such as a WSi layer, and the thickness of the WSi layeris about 1550 to 1650 Å. The thickness of the insulating layer 204, suchas silicon oxide layer, is about 750 to 850 Å. The thickness of thefirst dummy poly layer is about 950 to 1050 Å. The thickness of theinsulating layer 206, such as silicon nitride layer, is about 250 to 350Å. The material of the insulating layer 206 is different from theinsulating layer 204. The width of the opening 208 is 0.18 μm.

[0018] In FIG. 2b, the insulating layer 206 and the first dummy polylayer 205 are anisotropically etched by reactive ion etching or plasmaetching until the insulating layer 204 is exposed to form a firstwordline mask 209 a, a second wordline mask 209 b, and an opening 209 cin between. A width of the first wordline mask 209 a and the secondwordline mask 209 b are both 0.14 μm.

[0019] In FIG. 2c, a insulating layer 210 is conformably formed to coverthe first wordline mask 209 a, the second wordline mask 209 b, and theopening 209 c. The thickness of the insulating layer 210, such as thenitride layer, is 200 Å, and the material of the insulating layer 210 isthe same as the insulating layer 206.

[0020] In FIG. 2d, the insulating layer 210 is anisotropically etched byreactive ion etching or plasma etching until the insulating layer 204 isexposed to form a spacer 210 a on a sidewall of the opening 209 c.

[0021] In FIG. 2e, a second dummy poly layer 211 acting as a sacrificiallayer is conformably formed to cover the first wordline mask 209 a, thesecond wordline mask layer 209 b, and the opening 209 c, and the opening209 c is filled with the second dummy poly layer 211. The thickness ofthe second dummy poly layer is 2000 Å.

[0022] In FIG. 2f, the second dummy poly layer 211 is etched to exposethe insulating layer 206 and below than the spacer 210 a.

[0023] In FIG. 2g, the insulating layer 206, the spacer 210 a, and theexposed insulating layer 204 are removed to form a third wordline mask209 d in the opening 209 c, the third wordline mask 209 d is composed ofthe second dummy poly layer 211 a and the insulating layer 204 a. Thewidth of the third wordline mask 209 d is 0.14 μm. The first wordlinemask 209 a, the third wordline mask 209 d, and the second wordline mask209 b are disposed apart by a predetermined distance of 200 Å.

[0024] In FIG. 2h, the metal layer 203 and the poly layer 202 areanisotropically etched by reactive ion etching or plasma etching usingthe first wordline mask 209 a, the second wordline mask 209 b, and thethird wordline mask 209 d as etching masks until the semiconductorsubstrate 201 is exposed to form a first wordline 212 a, a secondwordline 212 b, and a third wordline 212 c. The first wordline mask 209a, the second wordline mask 209 b, and the third wordline mask 209 d areremoved.

[0025] An additional wordline 212 c is formed between the previouswordlines 212 a and 212 b of the present invention, the space 213 is notlimited by the characteristics of the light source and the photoresistlayer and a distance is reduced to 200 Å. Therefore, the density of thewordline of the EEPROM is increased

[0026] While the invention has been described by way of example and interms of the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments. To the contrary,it is intended to cover various modifications and similar arrangements(as would be apparent to those skilled in the art). Therefore, the scopeof the appended claims should be accorded the broadest interpretation soas to encompass all such modifications and similar arrangements.

What is claimed is:
 1. A method for forming a double density wordline,comprising: providing a semiconductor substrate; sequentially forming apoly layer, a first insulating layer, a first sacrificial layer, asecond insulating layer, and a photoresist layer with a wordline patternon the semiconductor substrate; sequentially etching the secondinsulating layer and the first sacrificial layer using the photoresistlayer as an etching mask until the first insulating layer is exposed toform a first wordline mask, a second wordline mask, and an openingtherebetween; removing the photoresist layer; forming a spacer on asidewall of the opening; forming a second sacrificial layer in theopening; removing the spacer, the second insulating layer, and the firstinsulating layer under the spacer to form a third wordline mask composedof the second sacrificial layer and the first insulating layerthereunder; and etching the poly layer to form a first wordline, asecond wordline, and a third wordline using the first wordline mask, thesecond wordline mask, and the third wordline mask as etching masks. 2.The method for forming a double density wordline of claim 1, furthercomprising a silicide layer over the surface of the poly layer.
 3. Themethod for forming a double density wordline of claim 2, wherein thesilicide layer is a tungsten silicide layer.
 4. The method for forming adouble density wordline of claim 3, wherein a thickness of the tungstensilicide layer is 1550 to 1650 Å.
 5. The method for forming a doubledensity wordline of claim 1, wherein a thickness of the poly layer is1150 to 1250 Å.
 6. The method for forming a double density wordline ofclaim 1, wherein the first insulating layer is a silicon oxide layer. 7.The method for forming a double density wordline of claim 6, wherein athickness of the silicon oxide layer is 750 to 850 Å.
 8. The method forforming a double density wordline of claim 1, wherein the firstsacrificial layer is a poly layer.
 9. The method for forming a doubledensity wordline of claim 8, wherein a thickness of the poly layer is950 to 1050 Å.
 10. The method for forming a double density wordline ofclaim 1, wherein the second insulating layer is a nitride layer.
 11. Themethod for forming a double density wordline of claim 10, wherein athickness of the nitride layer is 250 to 350 Å.
 12. The method forforming a double density wordline of claim 1, wherein the spacer is anitride layer.
 13. The method for forming a double density wordline ofclaim 1, wherein the second sacrificial layer is a poly layer.
 14. Amethod for forming a double density wordline, comprising: providing asemiconductor substrate with a poly layer, a silicide layer, a oxidelayer, a first dummy poly layer, and a first nitride layer; forming aphotoresist layer with a first opening on the nitride layer, wherein aportion of the first nitride layer is exposed by the first opening;sequentially etching the fist nitride layer and the first dummy polylayer until the oxide layer is exposed to form a first wordline mask, asecond wordline mask, and a second opening therebetween; removing thephotoresist layer; conformably forming a second nitride layer cover thefirst wordline mask, the second wordline mask, and the second opening;anisotropically etching the second nitride layer to form a spacer on asidewall of the second opening; forming a second dummy poly layer coverthe first wordline mask, the second wordline mask, and the secondopening, wherein the second opening is filled with the second dummy polylayer; etching the second dummy poly layer to a level below the spacer;removing the spacer, the first nitride layer, and the exposing oxidelayer to form a third wordline mask composes of the second dummy polylayer and the oxide thereunder; and sequentially etching the silicidelayer and the poly layer to form a first wordline, a second wordline, athird wordline using the first wordline mask, the second wordline mask,and the third wordline mask as etching masks.
 15. The method for forminga double density wordline of claim 14, further comprising a step toremove the first wordline mask, the second wordline mask, and the thirdwordline mask.
 16. The method for forming a double density wordline ofclaim 14, wherein a thickness of the poly layer is 1150 to 1250 Å. 17.The method for forming a double density wordline of claim 14, whereinthe silicide layer is a tungsten silicide layer.
 18. The method forforming a double density wordline of claim 17, wherein a thickness ofthe tungsten silicide layer is 1550 to 1650 Å.
 19. The method forforming a double density wordline of claim 14, wherein a thickness ofthe oxide layer is 750 to 850 Å.
 20. The method for forming a doubledensity wordline of claim 14, wherein a thickness of the first dummypoly layer is 950 to 1050 Å.
 21. The method for forming a double densitywordline of claim 14, wherein a thickness of the first nitride layer is250 to 350 Å.
 22. The method for forming a double density wordline ofclaim 14, wherein a thickness of the second nitride layer is 400 Å. 23.The method for forming a double density wordline of claim 14, whereinthe anisotropic etching is reactive ion etching or plasma etching. 24.The method for forming a double density wordline of claim 14, wherein athickness of the second dummy poly layer is 2000 Å.